1. Field of the Invention
This invention relates to the blocking of lenses for surfacing, edging or other finishing operations and has particular reference to improvements in blocks formed of eutectic materials which are cast in situ.
2. Discussion of the Prior Art
Lens blocking for surfacing and other finishing operations can be performed with exceptional ease and precision by casting blocks in place in a cavity defined on one side by the lens and all other sides by mold surfaces.
Eutectic metal alloys are preferred blocking media in view of their ease of handling, neatness in operation, sturdiness in use, and ease of removal and reclaim.
By such means, a fresh, i.e. completely newly formed, block is provided for the working of each lens thereby obviating the tedious, time-consuming and costly block cleaning, trueing, rebuilding and/or replacement of old art cast iron or steel blocks, not to mention the elimination of messy blocking adhesives such as pitch and associated apparatuses such as heating kettles and dispensers.
Heretofore, however, cast eutectic metal alloy blocks and blocking techniques have been beset with problems of overcoming the high cost of blocking materials without sacrifice of block strength.
An insufficiency of blocking material permits lens deformation and/or breakage under pressures of surfacing operations with attending high scrap yields while, on th other hand, greater amounts of blocking material and/or the use of higher eutectic point (more rigid) materials for greater block strength respectively increase material cost and the chances of heat deformation, cracking or other damaging of lenses. The latter, i.e. greater amounts and/or higher eutectic point materials, may be more deleterious to plastic lenses but are not without tendency to damage glass lenses, especially those of thinner cross-sections. The use of larger amounts of blocking material also increases costly oxidation and spill losses.
The foregoing and related drawbacks of prior art cast lens blocks and blocking techniques are overcome by the present invention wherewith high block rigidity may be accomplished with minimal amounts of casting material per block and a uniquely low transfer of heat to lenses being blocked.
It is, accordingly, a principal object of the invention to provide improved lens blocks and method of blocking lenses for fixturing to lens working equipment.